1. The Uranium Fuel Cycle Robert Tsai November 21, 2006

2. Overview Front end –Mining –Milling –Enrichment / fuel fabrication Service period Back end –Transport and storage –Disposal (open fuel cycle) –Reprocessing (closed fuel cycle)

3. Mining Processes World reserves: 3.1 million tU Open-pit mining: 30% Underground mining: 38% (55% in 1990) In situ leaching (ISL): 21%

4. Milling – Uranium Extraction Grinding (~100 microns) Acid (H 2 SO 4 ) or alkaline (Na 2 CO 3 / NaHCO 3 ) leach Solid / liquid separation of slurry Purification (simple or extensive) Precipitation – diuranate salt (e.g. Na 2 U 2 O 7 ) Drying Uranium oxide concentrate (UOC) (predominantly U 3 O 8 )

5. Milling – Uranium Conversion Dissolving of U 3 O 8 in HNO 3 Calcination (strong heating) → UO 3 Reduction with H 2 → UO 2 Hydrofluorination (HF) → UF 4 Fluorination (F 2 ) → UF 6 In most cases, end-use requires conversion to UF 6 for enrichment However, certain reactors (CANDU) can use “natural” UO 2

6. Enrichment Natural uranium: 235 U: 0.7%, 238 U: 99.3% Reactor-grade: 235 U increased to 3-5% –Necessary to sustain fission chain reaction Methods –Gas diffusion (GD) –High-speed gas centrifugation (GC) 5% of power requirements for GD –Laser technology (still in development) Afterward, UF 6 converted back to UO 2 for mechanical processing (fuel rods)

7. Service Period Fission process depletes fuel – 235 U → 92 Kr, 141 Ba – 238 U → 239 U → 239 Pu PWRs and BWRs reloaded bet/1-2 years, 1/4-1/3 of assemblies replaced Complicated optimization problem –Maximize core reactivity –Top priority to safety / operational limitations

8. Transport and Storage At Reactor (AR) storage –Handle intense radioactivity of freshly- discharged fuel –Wet (cooling ponds) vs. dry Transport via heavily-shielded flasks Away From Reactor (AFR) storage –Similar set-up to AR facilities NRC has repeatedly confirmed storages’ safety, minimal environmental impact

9. Disposal (Open Fuel Cycle) No permanent disposal procedures have been implemented in the world –Plans for 2010? Consensus: burial deep underground after period of interim storage –Safeguards: vitrification, corrosion-resistant canisters, constant monitoring (10 6 years) –U.S. waste: Yucca Mountain in Nevada

10. Reprocessing (Closed Fuel Cycle) Similar process as with fresh feed Benefits –Resource conservation –Decreased waste load –Use of ex-military material Uranium + plutonium → MOX fuel Major challenge: build-up of by-products

11. Conclusions Front end –Well developed and understood process –Gas centrifugation: best available enrichment technology –Future of lasers questionable Back end –Underground disposal viable but will always have critics –Reprocessing necessary but has limitations